Use of stem cells to regenerate or repair damaged/defective tissues is a promising strategy to cure many human diseases and disorders. Because the current protocols for purification of stem cells from dental tissues are labor intensive, somewhat vague and often expensive, the general objective of this proposal is to develop safe, simple and efficient techniques to purify stem cells from dental tissues. Adult stem cells have been identified in many tissues including dental pulps and dental follicles. One of the important purposes of stem cell's presence in adult tissues is to serve as the repair/regeneration system to replace damaged or defective tissues/organs. In order to fulfill the repair task, stem cells must first survive the conditions causing the damage. Thus, they are presumed to possess specific or extra defense or protection mechanisms that allow them to survive various stresses. Support for this theory includes evidence that certain stem cells are equipped with a high level of efflux proteins, such as ATP-Binding Cassette (ABC) transporters on their membrane to pump out harmful chemicals (Goodell et al., 1996;Wolf et al., 1993;Zhou et al., 2002), and that some stem cells produce high levels of cytosolic aldehyde dehydrogenases (ALDHs) to detoxify cellular aldehyde (Cai et al., 2004;Storms et al., 1999;Kastan et al., 1990). When subjected to hypoxia, stem cells grow more rapidly and form more colonies in hypoxic conditions than they do in normal oxygen atmosphere (Lennon et al., 2001) suggesting that stem cells can survive better in low oxygen stress. Based on the above, the overall hypothesis is that stem cells from dental tissues possess unique selfprotection/ defense abilities (i.e., anti-stress/drug mechanisms), and that this unique feature can be used to develop conditions that selectively kill/eliminate non-stem cells such that one could purify stem cells from heterogeneous cell populations. To test this hypothesis, heterogeneous cell populations from dental pulps and dental follicles will be subjected to medium containing selected substrates of BCRP or ALDHs. In addition, the heterogeneous populations will also be cultured under thermal and hypoxic conditions. The resulting subpopulation cells will be evaluated for stem cell properties. The optimal putative stem cell populations will be further studied for their molecular characteristics using microarray. Relevance: Dental damage (defect and loss of teeth) is a major health care issue in the United States. Stem cell technology provides a very promising strategy to repair or regenerate damaged/defective teeth. Development of safe, simple and efficient techniques to purify stem cells from dental tissues is the foundation for successfully use the strategy both in research and clinical aspects.